Which of the following substituted phenol is most acidic in nature?
(I) (II)
(III) (IV)

Question

Which of the following substituted phenol is most acidic in nature? (I) (II) (III) (IV)

TestHub · Accepted Answer

Nitro groups stabilise the phenoxide anion by resonance (from ortho and para positions) and by induction. Two nitro groups stabilise more than one, and three more than two. Compound (III), picric acid, carries nitro groups at 2, 4 and 6, so its conjugate base is the most stabilised (pKa ≈ 0.3) and (III) is the most acidic.

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